Current high pressure liquid chromatography shear valve systems typically employ a metallic stator element and a rotor device composed of a polymer material that forms fluid-tight seal at a rotor/stator interface therebetween. Depending upon the internal fluid pressures that these shear valve systems are designed to operate (typically 15 Kpsi or greater), as well as other environmental factors, these valves are typically capable of more than 15K, relatively maintenance free, cycles of use. Certain valve components, however, do wear over time such as the rotor seal and the stator seal. These valve components, fortunately, can be serviced or replaced, significantly extending the lifecycle of the valve.
Many multi-position, shear valve assemblies currently in use, including the next generation valve assembly 20 designs, shown in FIGS. 1-3, are typically rebuilt using the following technique. By simply removing the three socket head cap screws 21 that bolt the stator element 22 to the valve housing 25, the stator element 22 can be removed in order to access the rotor element 23. Using this technique, a service technician and/or end user can then easily replace both the rotor element and/or stator element. In this current valve configuration, loosening of the cap screws 21 is sufficient to simultaneously remove the sealing load (i.e., compression pressure) between the stator element 22 and the rotor element 23, at a rotor-stator interface, which is generated by a combination of a spring assembly 26 and a pressure adjuster nut 27 directly rotatably mounted to the valve housing 25.
Briefly, as shown in FIG. 2, as the pressure adjuster nut 27 is adjusted by rotating its head, relative to the valve housing 25, a distal portion of the pressure adjuster nut is axially advanced or retracted into contact with a proximal portion of the spring assembly 26. As the spring washers 28 of the spring assembly 26 are compressed, the generated compression force biases the rotor element into compressive contact with the stator element. When the valve is properly calibrated, via adjustment of the pressure adjusting nut 27, the rotor element 23 and the stator element 22 are sealed together at the interface in a fluid-tight manner to accommodate a selected fluid pressure flowing through the rotor channels and stator channels.
Accordingly, when the serviceable valve components are replaced, the stator screws 21 are reinserted and retightened. This requires tightening the stator screws 21 while simultaneously battling the compression force generated by the spring assembly 26 when the stator screws contact the stator element 22.
While this rebuild technique and valve design is satisfactory for the most part, several potential problems may be encountered during such field servicing unless the valve is field recalibrated; a procedure that significantly reduces an end users ability to self-rebuild the valve. For one, the pressure adjuster nut 27, at the proximal end of the shear valve assembly 20 could potentially be rotated, altering the factory “set” compression load. Furthermore, the end user may not properly tighten the stator screws 21 to the requisite torque requirements. In addition, since the stator element 22 is tightened against the rotor element 23, via the three stator screws 21, while a compression load is simultaneously generated at the rotor-stator interface via the spring assembly 26 and pressure adjuster nut 27, the stator element 22 may not properly seat flat and/or flush against a distal end edge of the stator ring 30. Due to any one of these variables, let alone in combination, the ability of the valve hold the required fluid pressure, at the interface, can greatly be affected.
Moreover, with the next generation ultra-high pressure, shear valve assemblies recently designed by Rheodyne (i.e., those capable of accommodating fluid pressures of 25 Kpsi or greater, and as shown in FIGS. 1-3), metallic stator elements and metallic rotor elements are applied, thus incorporating metal-on-metal sealing surfaces to improve durability and increase their lifecycle. With these metal-on-metal valves (disclosed in our U.S. Provisional Patent Application Ser. No. 61/225,143, filed Jul. 13, 2009, to Tower; 61/301,516, filed Feb. 4, 2010, to Tower; and 61/328,594, filed April, 2010, to Tower, all of which are entitled “ROTARY SHEAR VALVE ASSEMBLY WITH HARD-ON-HARD SEAL SURFACES”, and all of which are incorporated by reference in their entirety), it has been observed that the proper amount of compression force being applied by the pressure adjuster nut is very critical. Another design challenge observed with these metal-on-metal sealing surfaces is that the perpendicularity (or flushness) of the stator element 22 to the rotor element 23 is also very important to maintain a fluid-tight sealing surface under high pressure fluid loads. Even slight surface variations on the order of only 0.005″ can cause the shear valve to hold thousands of PSI less than when new or can cause premature valve failure.
Accordingly, the ability to reproduce the factory set compression pressure, as well as the ability to assure a substantially flat seat of the stator element 22 to the distal end edge of the stator ring 30, during a valve rebuild, is highly desirable.